1. Field of the Invention
This invention relates generally to electrically connecting one electronic component to another electronic component and, in particular, to providing a socketable bump grid array comprising shaped solder-coated metal spheres attached to one of the components which shaped solder-coated metal spheres are pluggable into sockets of the electronic component to be connected thereto.
2. Description of Related Art
Forming an electronic package whereby an electrical component such as an integrated circuit chip is electrically connected to a substrate such as a card, a board, another chip or any other electronic part is well-known in the art. Surface mount technology (SMT) has gained acceptance as the preferred means of joining electronic devices together, particularly in high end computers. As compared to more traditional pin connection methods, where a pin mounted to the backside of a ceramic module is thrust through a hole in the board, twice the number of modules can be placed on the same board area using SMT.
A myriad of solder structures have been proposed for the surface mounting of one electronic structure to another. Typical surface mount processes form the solder structures by screening solder paste on conductive, generally metallic pads exposed on the surface of a first electronic structure or substrate. A stencil printing operation is used to align the contact mask to the pads. The solder paste areas on the screened substrate are then aligned to corresponding pads on the electronic structure or board to be connected. After alignment, the substrate and board go through a reflow operation to melt the solder paste and create a solder bond between the corresponding pads on the substrate and board.
Other known surface mount technology uses solder balls rather than a solder paste to provide the solder connecting structures. By using solder balls, a more exact and somewhat greater quantity of solder can be applied than through screening. The solder balls are aligned and are held to a substrate and melted to form a solder joint on a conductive pad of the substrate. As before, the substrate with the newly joined solder balls is aligned to the board to be connected therewith and the solder balls are then reflowed to form a solder bond between substrate and board. The use of solder ball connectors has been applied to the mounting of integrated circuit chips using the so-called C-4 (control collapse chip connection) technology since the method and structure were first described and patented in U.S. Pat. Nos. 3,401,126 and 3,429,042 of Miller, which patents are assigned to the present assignee.
Solder ball connector (SBC) technology for multilayer ceramic components is designed for low cost, low induction surface mounting interconnection but is not currently pluggable into a second level socket. SBC is specifically designed for surface mount attach procedures since sockets typically require hard mating surfaces (like those found on pins) rather than the soft solder found on SBC's.
Socketing of SBC's is desirable on two accounts, however, the first is to provide module level burn-in of the semiconductor devices. The second is to provide a field upgradeable package similar to the Pin Grid Array (PGA). SBC-like packaging is being considered for X-86 and Power PC types of microprocessors and lack of pluggability remains a major hurdle to use of this technology.
In IBM Technical Disclosure Bulletin, AT 885-0235 (September 1986) the use of a copper ball surrounded by eutectic solder is shown as the joint structure for attaching a multilayer ceramic (MLC) substrate to a PC laminate wherein the ball serves as a standoff. A similar concept is described by Totta and Sopher for SLT technology as described in "SLT Device Metallurgy and Its Monolithic Extensions" IBM .JRD, Vol. 13, No. 3, pages 226-238, May 1969. Both techniques employ soldering together of two distinct components. Japanese patent no. 7,099,385 describes a manufacturing process of preventing crushing of an entire solder ball due to melting of solder and provides a simple connection structure in the gap between connection terminals by using a metallic sphere precoated with solder. The basic SBC structure and processes are described in U.S. Pat. Nos. 5,060,844 and 5,118,027, which patents are hereby incorporated by reference.
Bearing in mind the problems and deficiencies of the prior art, it is an object of the present invention to use solder ball connector technology to make electronic components having shaped socketable solder bump grid arrays for electrically connecting the electronic component to another electronic component.
It is a further object of the invention to provide an apparatus to fabricate a socketable bump grid array on an electronic component.
It is another object of the invention to provide a method for making a socketable solder bump grid array.
Other objects and advantages of the present invention will be readily apparent from the following description.